1. Field of the Invention
The present invention relates to amplifying a signal in general and to amplifying a signal using ramping in particular.
2. Discussion of the Related Art
High quality radio frequency (RF) signals must ramp quickly from a condition of minimal output power to a condition of information-bearing modulation at a specified output power and back down to the condition of minimal output power. Such power ramping capability is required for transmitters in many Time Division Multiple Access (TDMA) communication systems and other transmitters. Examples to such TDMA systems include those specified by the DECT, GSM and ansi-136 standards, and combinations of the same.
A fundamental requirement of these transmitters is that the acts of ramping up and ramping down must not violate specified limits on peak power in spectral bands away from the assigned RF channel. Such bands would be allocated to other transmitters. The associated measurement is called the transient spectrum in some systems or the transient adjacent channel power (transient ACP) in others.
In many cases, E class amplifiers comprise two transistors connected serially, to form a widely used cascode cell. In many cases, amplifier input signal is such the AC amplitude is higher than the DC amplitude, which makes difficult to disable the transmission. To achieve the disabling, the voltage value of the DC should be negative, which requires additional hardware modules, such as negative voltage generator.
FIG. 1A shows a graph of voltage provided to the amplifying unit, in accordance with an exemplary embodiment of a prior art transmitter. The normal operation DC voltage 110 is 0.5 to 0.7 volts, and the AC voltage 120 has amplitude of 1 volt or higher. The standard threshold voltage of the amplifier is about 0.5 to 0.7 v, which means that the DC voltage is required, to disable the amplification, has to be negative, such as negative DC voltage 130.
It is desired to provide a transmitter having an amplifying unit that avoids the requirement for negative power.